Methods of obtaining metal powder from ores or oxides



July13,1965 NAESER ETAL 3,194,648

state.

United States Patent O 3,194,643 METHODS F OBTANING METAL POWDER FRM GRES 0R OXIDES Gerhard Naeser, Duisburg, and Norbert Dautzenberg, Wattenscheid, Germany, assignors to Mannesmann Aktiengesellschaft, Dusseldorf, Germany, a corporation of Germany Filed July 9, 1963, Ser. No. 293,816 Claims priority, application Germany, July 30, 1962, M 53 734 The invention relates to metallurgy, and relates more particularly tomethods of obtaining metal powder-s from ores or oxides by their chemical reduction.

One of the principal objects of the invention is to provide a process for obtaining metal powders from ores or oxides by a series of steps followed by a reduction with a reducing substance.

It is a further object of the invention to include among the aforesaid steps an activation by means of mechanical treatment and the addition of a catalyst.

The invention accordingly comprises the several steps `and the relation of one or more of such steps with respect to each of the others, all as exemplified in the following detailed disclosure, and the scope `of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description, taken in connection with the accompanying dr-awings, in which the single view is a graph showing the rate of reduction of an oxide in percent for two different heating periods, plotted over milling time in minutes.

Most metals are today obtained by melting. For some special purposes, however, such as for instance the obtaining of spongy iron, there have been developed methods in which both ingredients, namely the metal oxide and the reduction carbon are brought to react in the solid The foregoing method has, however, to date not been used for economically and technically particularly important metals, such as ferrochromium, ferromanganese, or ferrovanadium.

The reduction :of the aforesaid oxides in their solid state can be carried out only in a vacuum. Such a process can be economical only, however, if it avoids too high temperatures as Well as too long times.

The instantY invention renders it possible to reduce not only the reaction temperatureconsiderably, but also to reduce markedly the reaction time. Broadly speaking, this is obtained by an accurately determined mechanical treatment and the addition of pre-determined small amounts of one or more catalysts.

Concentrated research of various reactions has yielded the insight that the reduction `of metal `oxides with solid or gaseous lreduction media can be advanced by a mechanical treatment of the solid particles prior to the reaction, for instance by rolling, hammering, or milling. As shown in the drawing, -this treatment leads alternatingly to an activation and passivation of the chemical reaction. In accordance with the invention, the reaction should be carried out at that milling time which corresponds to a maximum of reactivity. This optimum milling time depends on the con-struction and size of the mill, and needs to be determined with the aid of the graphs shown in the drawing.

The other step for reducing the reaction time is the addition of catalysts in the form of metal salts of alkalies and of alkaline earths; potassium fluoride and potassium carbonate have been found to be particularly suitable catalysts. The maximum effect is obtained with a definite yamount which lies between about 0.1 percent and 0.6 percent, and need-s to be determined separately for every material.

For the production of ferrochromium powder from a chromic iron ore, the following exemplified method may be used: A certain amount of carbon powder is added to the ore, the amount of the powder being that which is necessary for the reduction of the chromium and the iron. The ore and the powder are then milled in a ball mill for a predetermined time. The powder will be mashed into a stiff paste, with the aid of a solution which contains the necessary amount of potassium uoride, then dried and briquetted. After the heating, for reduction, in a vacuum, the briquettes will be comminuted, such as crushed, and the ferrochromium powder be separated from the slag powder in accordance with well-known suitable processes.

Example A chromic iron ore containing 15.5% iron `oxide and 60.87% chromium oxide was ground to a ne powder; 17% carbon powder was admixed, and the milling continued for one-half of one hour (0.5 hn). One kilogram (2.2 lbs.) of the foregoing mixture was mixed with cu. cm. (6.1 cu. in.) of an aqueous solution of potassium fluoride (1 normal). The mixture of the ore and the carbon after the drying conta-ined 0.59% potassium fluoride. Following the briquetting, the mixture was heated in a vacuum of about 0.1 mm. Hg and a temperature of 1300 C. (2372 F.) for 10 hours. In order to avoid too much gas yield and the resultant detrimental loosening of the reaction mixture, the heating to the reaction temperature must be correlated to the occurring gas generation. After the resultant mixture has been cooled, the metallic ferrochromium powder must be separated from the slag powder. This separation was carried out, following a comminution of the heated product, simply with the -aid of a magnetic separator. The metal thus obtained had about 61% chromium and 0.4% carbon. For the complete elimination of the carbon, the ferrochromium metal was powdered, then mixed with 2% chromic oxide (Cr203) and 0.1% of potassium uoride admixed, and thereafter again heated at a temperature of from 1200 C. (2192 F.) and 1300 C. (2372 F.). The resultant products are strongly sintered, practically carbon-free briquettes immediately usable for the alloying in steel production.

Since certain changes in carrying out the above process could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

Having thus described the invention, what we claim as new and desire to be secured by Letters Patent, is as follows:

1. A method of obtaining ferrochromium metal powder from chromic iron ore comprising comminuting said chromic iron ore to a line powder;

mixing said finely powdered chromic iron ore with carbon powder and subjecting the resulting mixture to continued grinding;

blending into the resulting mixture 0.1 to 0.6%, based on the weight of said mixture, of a catalyst selected form the group consisting of metal salts of alkalies and of salts of alkaline earths, said salts being added in the form of an aqueous solution;

drying and briquetting said mixture;

heating the resulting briquettes under vacuum to about 1300o C. to bring about reduction of the chromic i-ron ore to ferrochromium;

cooling and comminuting the reduced ore;

and subsequently separating the ferrochromium metal powder from the slag.

2. A method according to claim 1 in which said catalyst is potassium fluoride which is being present in the dried mixture in an amount of about 0.59% by Weight.

3. A. method as claimed in claim 1, in which the ferroehromium powder separated from the slag is mixed with about 2% by weight of Cr2O3 and about 0.1% by weight of potassium fluoride and then heated to a temperature in the range between 1200 and 1300 C., in order to eliminate the carbon present in said ferrochromium powder.

Reerenees Cited by the Examiner UNITED STATES PATENTS 2,108,043 2/ 38 Crist 75-33 2,290,734 7/42 Brassert 75-208 2,380,405 7/45 Buehl 75-33 3,068,090 12/62 Reed et al 75-33 3,097,945 7/63 Paris et al. 75-5 FGREIGN PATENTS 645,030 10/50 Great Britain.

CARL D. QUARFORTH, Primary Examiner. REUBEN EPSTEIN, Examiner. 

1. A METHOD OF OBTAINING FERROCHROMIUM METAL POWDER FROM CHROMIC IRON ORE COMPRISING COMMINUTING SAID CHROMIC IRON ORE TO A FINE POWDER; MIXING SAID FINELY POWDERED CHROMIC IRON ORE WITH CARBON POWDER AND SUBJECTING THE RESULTING MIXTURE TO CONTINUED GRINDING; BLENDING INTO THE RESULTING MIXTURE 0.1 TO 0.6%, BASED ON THE WEIGHT OF SAID MIXTURE, OF A CATLYST SELECTED FORM THE GROP CONSISTING OF METAL SALTS OF ALKALIES AND OF SALTS OF ALKALINE EARTHS, SAID SALTS ADDED IN THE FORM OF AN AQUEOUS SOLUTION; DRYING AND BRIQUETTING SAID MIXTURE; HEATING THE RESULTING BRIQUETTES UNDER VACUUM TO ABOUT 1300*C. TO BRING ABOUT REDUCTION OF THE CHROMIC IRON ORE TO FERROCHROMIUM; COOLING AND COMMINUTING THE REDUCED ORE; AND SUBSEQUENTLY SEPARATING THE FERROCHROMIUM METAL POWDER FROM THE SLAG. 